The present invention relates to devices and methods for the control of blood flow or the flow of other body fluids in the extracorporeal treatment of the blood or other fluid. More particularly, the invention relates to devices and methods for the control of blood flow or the flow of other body fluids in extracorporeal treatment through pumping the blood or other fluid with alternating positive and negative pressures applied to the blood flow circuit or body fluid flow circuit of a treatment apparatus. The invention also relates to devices and methods for the withdrawal of blood or other fluid from a patient by applying alternating positive and negative pressures to a fluid flow line.
Present extracorporeal blood treatment devices, such as hemodialysis, hemodialysis with a sorbent suspension, push-pull plasmapheresis, plasmafiltration, hemofiltration and liver dialysis machines, as well as machines for blood irradiation and phototherapy treatment, hyperthermia, hypothermia, blood gas management, etc., all have a common feature, in that they draw blood from a patient at as fast a rate as is practical, circulate the blood through a treatment unit, and then return the treated blood to the patient. This circulation of what amounts to essentially the whole blood supply of a patient outside the patient's body for treatment begins and ends with the passage of the blood through a single or dual lumen catheter system, generally assisted by a pump to increase the rate of blood flow, as well as to provide a regulated flow of blood throughout the treatment. Previous systems most typically use roller pumps set to a specified rate, which is carefully monitored and controlled by an attending nurse or physician, or by the user in home-use dialyzers.
Other treatment protocols, as for example, peritoneal dialysis, also involve the withdrawal of fluid from a patient in large volumes for disposal or for treatment by the action of an extracorporeal treatment device. Such other treatments, likewise, depend on the efficient drawing of a fluid from the patient without causing injury, and in some cases, circulating the fluid through a treatment unit, and returning the treated fluid to the patient.
A significant problem that often arises in extracorporeal blood treatments is venous collapse. The risk of collapse necessitates the careful monitoring of the blood pump by trained personnel. If the blood flow from the patient slows to below the rate at which the blood pump is operating, vacuum pressure builds in the patient access line. If this vacuum is too great, the vein around the catheter can collapse, stopping the blood flow. Continued pump action on the collapsed vein can cause damage to the veins, excessive bruising, and may require the catheter to be relocated to a new vein. Excessive vacuum pressures can also cause blood clotting in the dialyzer or other treatment unit, as well as hemolysis. For this reason, blood treatments are usually started at a sub-optimum blood flow rate, which is then slowly increased as the patient's veins will allow. The required monitoring places additional burdens on attending nurses and physicians, as well as increased risks on the patients. The skill level and attention requited in monitoring also limits the use of in-home treatment systems operable by the patients themselves.
A similar risk in the withdrawal of other fluids from the body, is the collapse of tissue surrounding the catheter, blocking the flow of the body fluid into the catheter and potentially causing bruising or other tissue damage.
It is evident there remains a need for improved devices and methods for withdrawal and extracorporeal treatment of blood or other body fluids, particularly for control devices that reduce the risk of venous collapse and tissue collapse, while maximizing the flow rate of blood or other fluid for any given patient, thereby minimizing the burden of monitoring the flow.